A cre-containing cassette including a nuclear localization signal and a polyadenylation sequence was inserted into the start codon of the LHRH gene by homologous recombination of the BAC, RP23-
22J8 which includes 137 kb of 5' upstream and 73 kb downstream sequences around the LHRH coding sequence of the BAC. The modified BAC was then used to create transgenic mice.